Regular Expression

Regular Expression Glossary

Table 1: Anchoring Metacharacters

Metacharacter	Description
^	Anchor the expression to the start of a line
$	Anchor the expression to the end of a line

Table 2: Quantifiers, or Repetition Operators

Quantifier	Description
*	Match 0 or more times
?	Match 0 or 1 time
+	Match 1 or more times
{m}	Match exactly m times
{m,}	Match at least m times
{m, n}	Match at least m times but no more than n times

Table 3: Predefined POSIX Character Classes

Character Class	Description
[:alpha:]	Alphabetic characters
[:lower:]	Lowercase alphabetic characters
[:upper:]	Uppercase alphabetic characters
[:digit:]	Numeric digits
[:alnum:]	Alphanumeric characters
[:space:]	Space characters (nonprinting), such as carriage return, newline, vertical tab, and form feed
[:punct:]	Punctuation characters
[:cntrl:]	Control characters (nonprinting)
[:print:]	Printable characters

Table 4: Alternate Matching and Grouping of Expressions

Metacharacter		Description
|	Alternation	Separates alternates, often used with grouping operator ()
( )	Group	Groups subexpression into a unit for alternations, for quantifiers, or for backreferencing (see "Backreferences" section)
[char]	Character list	Indicates a character list; most metacharacters inside a character list are understood as literals, with the exception of character classes, and the ^ and - metacharacters

Table 5: The REGEXP_LIKE Operator

Syntax	Description
REGEXP_LIKE(source_string, pattern [, match_parameter])	source_string supports character datatypes (CHAR, VARCHAR2, CLOB, NCHAR, NVARCHAR2, and NCLOB but not LONG). The pattern parameter is another name for the regular expression. match_parameter allows optional parameters such as handling the newline character, retaining multiline formatting, and providing control over case-sensitivity.

Table 6: The REGEXP_INSTR Function

Syntax

Description

REGEXP_INSTR(source_string, pattern [, start_position [, occurrence [, return_option [, match_parameter]]]])

This function looks for a pattern and returns the first position of the pattern. Optionally, you can indicate the start_position you want to begin the search. The occurrence parameter defaults to 1 unless you indicate that you are looking for a subsequent occurrence. The default value of the return_option is 0, which returns the starting position of the pattern; a value of 1 returns the starting position of the next character following the match.

Table 7: Explanation of 5-digit + 4 Zip-Code Expression

Syntax	Description
	Empty space that must be matched
[:digit:]	POSIX numeric digit class
]	End of character list
{5}	Repeat exactly five occurrences of the character list
(	Start of subexpression
-	A literal hyphen, because it is not a range metacharacter inside a character list
[	Start of character list
[:digit:]	POSIX [:digit:] class
[	Start of character list
]	End of character list
{4}	Repeat exactly four occurrences of the character list
)	Closing parenthesis, to end the subexpression
?	The ? quantifier matches the grouped subexpression 0 or 1 time thus making the 4-digit code optional
$	Anchoring metacharacter, to indicate the end of the line

Table 8: The REGEXP_SUBSTR Function

Syntax	Description
REGEXP_SUBSTR(source_string, pattern [, position [, occurrence [, match_parameter]]])	The REGEXP_SUBSTR function returns the substring that matches the pattern.

Table 9: The REGEXP_REPLACE Function

Syntax	Description
REGEXP_REPLACE(source_string, pattern [, replace_string [, position [,occurrence, [match_parameter]]]])	This function replaces the matching pattern with a specified replace_string, allowing complex search-and-replace operations.

Table 10: Backreference Metacharacter

Metacharacter		Description
\digit	Backslash	Followed by a digit between 1 and 9, the backslash matches the preceding digit-th parenthesized subexpression. (Note: The backslash has another meaning in regular expressions; depending on the context it can also mean the Escape character

Table 11: Explanation of Pattern-Swap Regular Expression

Regular-Expression Item	Description
(	Start of first subexpression
.	Match any single character except a newline
*	Repetition operator, matches previous . metacharacter 0 to n times
)	End of first subexpression; result of the match is captured in \1 (In this example, it's Ellen.)
	Empty space that needs to be present
(	Start of the second subexpression
.	Match any single character except a newline
*	Repetition operator matches the previous . metacharacter 0 to n times
)	End of second subexpression; result of this match is captured in \2 (In this example, it stores Hildi.)
	Empty space
(	Start of third subexpression
.	Match any single character except a newline
*	Repetition operator matches . metacharacter 0 to n times
)	End of third subexpression; result of this match is captured in \3 (In this example, it holds Smith.)

Table 12: Explanation of the Social Security Number Regular Expression

Regular-Expression Item	Description
^	Start of line character (Regular expression cannot have any leading characters before the match.)
(	Start subexpression and list alternates separated by the | metacharacter
[	Start of character list
[:digit:]	POSIX numeric digit class
]	End of character list
{3}	Repeat exactly three occurrences of character list
-	A hyphen
[	Start of character list
[:digit:]	POSIX numeric digit class
]	End of character list
{2}	Repeat exactly two occurrences of character list
-	Another hyphen
[	Start of character list
[:digit:]	POSIX numeric digit class
]	End of character list
{4}	Repeat exactly four occurrences of character list
|	Alternation metacharacter; ends the first choice and starts the next alternate expression
[	Start of character list
[:digit:]	POSIX numeric digit class.
]	End of character list
{9}	Repeat exactly nine occurrences of character list
)	Ending parenthesis, to close the subexpression group used for alternation
$	Anchoring metacharacter, to indicate the end of the line; no extra characters can follow the pattern